Similarities exist between vascular development processes and vascular diseases with significant angiogenic components, yet the nuclear signaling mechanisms regulating these processes are poorly understood. As a receptor for vascular endothelial growth factor, KDR/flk-1 has a central role in the formation of blood vessels in health and disease, and the results of gene deletion studies in mice demonstrate the critical developmental role of this gene. The hypothesis of this project is that transcriptional mechanisms regulating key developmental genes such as KDR/flk-1 are recapitulated in vascular diseases, and therefore may serve as targets for the understanding and treatment of these diseases. We have completed the initial characterization of the transcriptional mechanisms regulating KDR/flk-1 expression, and have begun to define specific transcriptional factors involved. The present proposal exploits well-characterized aspects of gene regulation, such as DNA-protein interactions and alterations in chromatin structure, as tools to explore further the mechanisms of KDR/flk-1 expression. These tools will allow us to study specific cis-actin elements and trans-acting that regulated KDR/flk-1 in vivo and in vitro in AIM I. It is likely that these DNA- binding proteins will be novel and will have a central role in endothelial cell differentiations from hemangioblastic precursors. The function of one identified transcriptional factor, EPASl, will be dissected in AIM II. Finally, we will begin to explore the role of transacting factors such as EPAS1 and others identified in AIM I in an in vivo model of tumor angiogenesis in AIM III, with a goal of testing the hypothesis that developmental and pathologic vascular processes share fundamental similarities at the gene transcription level. The score of this proposal is intended to address relevant biological and physiological questions using state of the art molecular biology techniques. Knowledge gained from this proposal should provide crucial information about endothelial cell development from multi-potent precursors, blood vessel formation in health and disease, and endothelial cell-type specific gene expression. In addition, mechanisms for targeted gene delivery to endothelial cells and for disruption of angiogenesis in its pathologic forms may be revealed.